The present invention is directed to a process for forming a latex polymer containing an ethylenically unsaturated derivatives of fatty acids and/or oils. More particularly, the present invention is directed to a process for forming a latex polymer which is produced by a staged polymerization process.
One problem encountered by coatings manufacturers is the development of formulations containing low VOC-coalescing aids or plasticizers. For instance, emulsion polymers are currently formulated with coalescing aids or plasticizers in order to form films at and below ambient conditions yet dry to films of sufficient glass transition temperature (Tg) to perform adequately at and above room temperature. In general, the ability of emulsion polymers to form or coalesce into film is governed by the minimum film forming temperature (MFT) of the polymer in question. Low MFT polymers are required in order to exhibit coalescence, flow, and surface wetting properties. However, if the polymer remains soft and tacky, the coatings are not usable. Therefore, it is necessary to develop a technology in which coating formulations contain suitable ingredients to provide an initial low MFT, which, upon application, form nontacky, durable, hard, and water resistant surfaces having a Tg significantly above their MFT.
Various other coating compositions which cure under ambient conditions are known in the prior art. A few such examples involve curing by a chemical reaction such as epoxide-carboxylic acid reaction, isocyanate-moisture reaction, polyaziridine-carboxylic acid reaction, and activated methylene-unsaturated acrylic reaction.
Recently, a number of new latex or emulsion compositions derived from semi-drying and/or non-drying oils have been developed for use in coatings, adhesives and inks. Such compositions are disclosed in U.S. Pat. Nos. 6,001,913; 6,174,948; and 6,203,720 each of which is incorporated herein by reference in its entirety.
The copolymerization of vinyl acetate with ethylenically unsaturated derivatives of fatty acids and/or oils via conventional emulsion polymerization techniques led to surprisingly low molecular weight polymers with poor film properties. Moreover, the uniquely large structure and high molecular weight of the ethylenically unsaturated derivatives of fatty acids and/or oils placed special demands on the surfactant choice.
Accordingly, it would be an advancement in the art to provide an economical process for co-polymerizing an ethylenically unsaturated monomer suitable for forming a latex polymer with ethylenically unsaturated derivatives of fatty acids and/or oils to form polymers that can be used in low VOC latex or emulsion compositions.